1. Field of the Invention
This invention relates to identification remote control and, in particular, it consists of an interrogator/receiver and a passive transponder. This group allows the univocal identification of a still or moving object, animal or person by producing a coded identification signal in answer to a signal sent by the interrogator/receiver that is inductively coupled with the transponder.
2. Description of Prior Art
Some remote control identification systems have already been proposed and used in which an interrogator acts to generate an A.C. clock signal that also acts as a power signal. By means of an inductive coupling, a transponder receives said signal and uses it as its power supply, thus generating a coded reply signal that is picked up by the interrogator/receiver. The coded signal is characteristic to that transponder, thus the object, animal or person, to which the transponder is associated can easily be recognized by the interrogator.
Particularly, in the device described in the patent application WO 85/03831, the clock signal sent by the interrogator and received by the transponder by means of the inductive coupling is at first reduced in frequency, then its frequency is further divided (for instance by eight or ten). An alternate current signal is thus produced having a frequency varying between two values; any variation from a frequency to another represents a value of "zero" or "one".
The encoding of this signal is obtained by means of a Manchester encoder, while its modulation is carried out by means of FSK system (frequency shift keying). The modulated signal returns to the interrogator by means of an inductive coupling, it is filtered through bandpass filters which partially eliminate the background noise, then it is sent to a FSK demodulator capable of recognizing the frequency variations of the signal. Then a microcomputer extracts the identification code and is able to transfer it to a monitor, a printer, a disk or other storage systems or to another computer.
The main disadvantage of this device is the need to use, for isolating the signal sent by the transponder, bandpass filters having a frequency band width at least equal to the difference between the two frequency values of the signal. In this way the background noise having a frequency comprised between the modulated signal frequency values, is allowed to pass through the filters and the recognition of the identification signal is sometimes difficult, particularly in a highly electromagnetically disturbed environment. Thus only the reduction of the maximum allowable distance between the interrogator and the transponder allows a sure identification.
Moreover, the device employs unalterable memories therefore its use is limited to simple identification systems.